Female butterflies face winter courtship woes

Some female butterflies adopt the mating patterns of their male counterparts in certain conditions, a new Yale study shows.

Yale researchers published a study in the Jan. 7 issue of the
journal Science that discovered that the temperature during larval
development causes a gender role reversal among African Bicyclus
anynana butterflies. While male butterflies that were raised in wet,
warm conditions court females, the study found that in the cold dry
season female butterflies flash their spots — a behavior usually only
performed by the males. Researchers said the results have larger
implications for trends in other insects that have yet to be explored.

“This was the first study to document a complete reversal across a
species that is temperature-based,” co-author Antonia Monteira said.
“It is interesting how environment has a profound effect in wiring the
insect brain to command courtship behavior in one sex or another.”

The study was conducted by Monteira’s lab in the Department of
Ecology and Evolutionary Biology and that of physics professor Hui Cao
to prove that males in the wet season and females in the dry season
actively court the opposite sex by using their pupils, the center of
their eyespots, to reflect UV light. Eyespots are concentric rings on
the wings of a butterfly that give off visual signals to attract mates,
said Kathleen Prudic, of Monteira’s lab.

“One of the quandaries was why were there eyespots in both sexes,” Prudic said, because usually only males use them.

Approximately 500 butterflies were studied to investigate the effect temperature has on mating patterns, Prudic said.

Monteira’s lab observed that females raised in the dry season
display eyespots to males, who choose females with brighter spots,
indicating the gender role reversal, she said.

Cao’s lab found that the brightness of pupils changed across seasons
by measuring the intensity of UV reflectivity of the pupils. Males from
the dry season had duller pupils than the courting male butterflies
from the wet season, while an opposite trend was observed among
females, she said.

The researchers also found that dry-season male butterflies are more
selective and more popular among female butterflies because their
spermatophore, the mass of sperm and various nutrients given to females
as a nuptial gift, is better than it is in the wet season.

The study was funded by the American Association of University Women and the Yale Institute of Biospheric Studies.